Cold facts behind the small eruption that left us under a cloud

The ongoing restrictions on flights in to and out of the UK mean holidaymakers, school parties and business travellers are either stranded elsewhere in the world or sitting at home frustrated that

their trip has not happened.

Since last Thursday, more than 63,000 flights in European airspace have been cancelled and more than two million passengers have been prevented from flying in or out of the UK. The UK's airlines are estimated to be losing 123m a day, and Easyjet alone says it has lost around 40m with the cancellation of more than 4,500 flights so far.

Wounded British troops travelling home from Afghanistan have been diverted to American bases in the Middle East. People with respiratory problems have been told to keep their medication with them. Imports and exports have been affected, and we may see supermarket shelves around Europe empty of vegetables, fruit and flowers normally flown in at this time of year from Africa.

International meetings and conferences have suffered, and some sporting events such as the ICC World Twenty20 in the Caribbean may have to manage without the England side if flying restrictions are not lifted in time for travel next weekend. Domestic tourism seems to be benefiting from the lockdown, though – the Lake District is

experiencing a sudden 35 per cent surge in bookings compared to this time last year.

All this is as a result of a relatively small eruption compared to the powerful Mount St Helens event in Washington State in1980 or the Mount Pinatubo eruption in the Phillipines in 1991. The difference here is an unlucky and unpredictable set of circumstances that means our science and technology-driven world is held to ransom by Mother Nature.

The eruption is causing such spectacular problems because it is taking place beneath an ice cap. This means the molten magma hits ice and water, causing it to cool very quickly – a process which means it is pounded into tiny fragments. The ash is then blown up into the sky by steam fountains created by evaporating ice. Larger lumps of ash fall in the local area, and the clouds of finer ash are lifted high into the sky and carried away by air currents. This "ash" is actually made up of tiny glass particles that cause a threat to aircraft.

"Much more powerful eruptions of larger volcanoes have not caused such widespread disruption in the past because the circumstances were different," says geologist and magma expert Professor Marjorie Wilson, of the department of earth and environment at Leeds University.

"The ash combines with two vital factors – the position of jet streams carrying the ash towards the UK, and the fact that the skies in this part of the world are among the busiest in the world, including a huge amount of transatlantic traffic." Professor Wilson says there was a volcanic eruption in north-east Iceland in 1783 which was so large that it sent a sulphurous smog up 1,000 feet into the air, which travelled south and killed an estimated 10,000 people across Europe, mostly by wiping out vegetation and causing starvation.

The last eruption of the volcano that's currently causing a black pall over southern Iceland was in December 1821, and lasted two years. It's not known exactly for how much of that period it was sending fountains of ash high above the clouds.

"We now live in a world of planes that fly high and have the unlucky combination of the relative locations of Iceland and UK and the prevailing winds carrying the ash along at the same level as the aircraft usually fly," says Prof Wilson. "It was bound to happen, sooner or later. There are volcanos elsewhere in the world – like the one in Montserrat in the Caribbean – which erupt on and off for years, but because the same circumstances do not prevail, there are emergencies, but generally life does go on around them."

While it is dangerous to say that the authorities are being over-cautious in continuing flight restrictions, the longer the crisis continues the more the airlines will push for proof of the real threat to aviation caused by the volcanic ash, says Robert Mayer, senior lecturer in transport management at Huddersfield University.

"The truth is that no-one knows the real impact. Even aviation authorities don't know the true effect of the ash on engines. In the meantime, the more robust airlines, like Lufthansa, will feel some damage but have enough cash reserves to survive. "

The good news in the short-term, says forecaster Rachel Vince at MeteoGroup, is that the north to north-westerly winds that have so far blown the volcanic ash directly down towards the UK are set to change this weekend and take a more south-westerly direction towards the North Pole and Scandinavia.

"The risk (of ash over the UK) looks to be lower for the next fortnight thanks to the change in wind direction. But if the volcano becomes more active and the wind changes again, then there will be more ash."